The invention generally pertains to laser light sources. More particularly the invention pertains to vertical cavity surface emitting lasers (VCSELs), integrated with detectors to be used to monitor and control the intensity of the VCSEL, and methods for producing such devices.
The electrical properties of lasers vary over time due to variance in manufacturing tolerances, environmental effects such as temperature or humidity and the age of the laser. Control of power output and bias conditions enhances performance of semiconductor lasers. Control of power output also allows relaxation of manufacturing tolerances, thus increasing the yield of useful devices. In fiber optic applications, the desired power output is the highest value consistent with eye safety and long-term reliability. It is common practice to monitor the output power of the laser and feedback a portion of the signal to circuitry that controls the operating conditions of the device. A critical requirement is that the ratio of the feedback signal to the coupled power output be constant. The problem arises in maintaining a relationship between the feedback and output that is linear for maintaining a constant proportional output under varying conditions of the VCSEL.
Davis, U.S. Pat. No. 6,069,905, which is incorporated herein by reference, offers one solution to this problem. Davis discloses a device to monitor laser output. This method uses a can package to house a partially reflective surface. The partially reflective surface is configured to direct some of the laser output through the surface to the optical fiber, and reflect the remainder of the laser output to a detector. The amount of light that is received at the detector can then be used to monitor the intensity of the laser and control its output. This approach is quite capable of monitoring and controlling the output of a single laser. However, this device can encounter problems if configured with an array of lasers, as the diverging light from other lasers could be captured by the wrong detector.
Zhou, U.S. Pat. No. 6,081,638 also offers a method of monitoring laser output with an integrated detector. Zhou discloses an optical fiber with a reflective coating on the cleaved end of the fiber. Most of the light that hits the end of the optical fiber enters the fiber, but some will be reflected off of the reflective coating. The device is configured in such a way that a detector monitors the reflected light. This device requires the optical fiber to be modified, which may not always be desirable.
As a result, there is a need for a device that can monitor and control laser output of lasers contained in an array without modifying the optical devices they feed.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The invention offers a device for monitoring and controlling the output of light sources. The invention includes devices to monitor light output from a light source, one embodiment of which includes: a V-groove substrate with a reflective coating deposited on at least one surface; an optical fiber; a light source positioned so that an amount of the produced light, which is less than 100%, enters the optical fiber; a light intensity or source detector positioned so that at least some of the produced light from the light source, that did not enter the optical fiber impinges upon the light intensity detector; and feedback circuitry.
Preferably, the light intensity detector utilized is a semiconductor detector and more preferably is a PIN detector. Preferably, the device of the invention is arranged within an array of devices.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.